The sporangiophore of Phycomyces responds in minutes to light, to stretch, to gravity and to the presence of nearby objects. The behavior is now well characterized and many hundreds of mutants are available and classified into complementation groups. We are attempting to correlate biochemical events with the known behavioral parameters by a combination of genetics and biochemistry. Cyclic AMP levels decrease upon light stimulation and return before the light response. In certain mutants both responses are abnormal. Changes in Cyclic GMP and in polyamines were also noted. Adenylate cyclase has characteristics in common with higher eucaryotes such as a striking sensitivity to dopamine. Dopamine seems to be present in Phycomyces and may serve a hormonal function. The cyclase is also sensitive in vitro to low light intensities. Phosphodiesterase is being characterized. A possible output enzymatic activity chitinase has been examined and was found to require a soluble activator. Hormonal and sensory processes are involved in sporangiophore development. Two areas of developmental biology were characterized: the amino acid distributions and amounts of change during maturation and chromosomal protein also change during sporangiophore development. Phycomyces may be an excellent model system to correlate sensory, hormonal and developmental systems.